The present invention relates generally to the field of printing. In particular, an apparatus for conforming a printing substrate to a printing zone of a printing platen in a large format ink jet print engine.
The present invention addresses a need in the art to simplify assembly and enhance operation of print engine components that interact with a printing substrate to ensure constant contact between a printing media relative to a print zone portion of a printing platen. In large format ink jet print engines one or more blowers coupled to a space having apertures in the printing zone of a platen offer some measure of uniformity for printing operations by creating a suction force which draws the printing media to the platen. Typically, such a suction force is used in addition to tensioned supply and take-up rolls alone or in conjunction with nip/grit roller assemblies driven by an axial shaft. It is known that if the media fails to adequately adhere to the platen while printing the carriage assembly, or a lower portion of print heads, can strike the media and damage either or both the media or the print heads at great cost of time and effort. In fact, oftentimes following such a xe2x80x9chead strikexe2x80x9d one or more print heads must be replaced due to the damage to the sensitive ink emitting nozzles typically disposed at the lowest portion of said print heads. At the least, a head strike causes loss of print media and ink used to reach the point at which contact occurs. In the event that a head strike occurs during overnight or unattended printing operations all later prints are typically lost and considerable damage to the print heads, carriage drive assembly, and the media often result.
Thus, as a result of the dire consequences attributed to head strikes, and the need for a consistent printing distance for consistent droplet placement, a variety of means for conforming a media to a platen surface have been utilized. The present invention improves on the systems previously utilized while at the same time conveniently solving difficult design issues related to evacuation of potentially harmful vapors, ink dust, and the like.
Driving a printing media through a printing zone using abrasive grit roller/nip roller combinations or with powered take-up media spools have long been known in the art of large format full color ink jet printing. And as long as the grit roller consistently cooperates with a corresponding nip roller to form a discrete, static location for the driving xe2x80x9cfootprintxe2x80x9d which propels the printing media at a constant velocity this technique has been basically successful. However, with the advent of large numbers of individual print heads operating in concert the printing zone necessarily increases in both length and width these prior art media handling mechanisms often fail to maintain conformity between media and platen surface. Any local deviations in the platen surface within the printing zone will typically produce repeatable printing errors in output because such local deviations are necessarily static in nature. Assuming that no other factor affects such deviations implies that the printing errors can be eliminated by characterizing the topography of the printing zone and correcting ink droplet trajectories to compensate for the deviation(s). However, in practice the media can xe2x80x9cwalkxe2x80x9d side to side during printing, the thickness of a given portion of a media web may vary, the rail supporting the print heads may change, the media may stretch from tensioned media drive systems, and the media may swell when receiving ink. Furthermore, the media may cup, distort, or kink as it advances due to a variety of factors; in particular, these types of errors has been observed to occur at the platen edges and near grit/nip roller locations where the media oftentimes bends. Prior art large format print engines were driven by necessity to apply a source of vacuum through the platen surface so that the media adhered to the platen in the critical printing zone. Other prior art large format print engines were equipped with slightly bowed printing zones (in the media web direction) and corresponding orientation of print emitting jets each disposed at the same distance from the printing zone.
Another potential source of error in large format ink jet printers relates to the fact that in the grit/nip roller equipped engines, the roller sets are typically driven by an axial shaft that must be manufactured to a very high straightness tolerance or else the footprint of the rollers on the media will remain the same size but rise and fall as the axial shaft rotates. This produces printing errors and may distort the media unnecessarily and can interfere with the effectiveness of any vacuum seal between the platen surface and the printing media.
The exemplary embodiment of the present invention taught herein address the failings of these prior art media handling mechanisms and the variety of other potential sources of printing error for large format ink jet print engines and is easily adapted for handling a wider variety of printing ink compositions than traditionally used in the large format ink jet printing industry.
The present invention thus finds utility over a variety of printing platforms that create a vacuum seal between platen and media through a vacuum supplied through apertures formed in a printing platen to promote a continuous sealing footprint over the entire printing zone.
The apparatus of the present invention thus increases the precision for controlling the movement of a printing media through an improved set of vacuum apertures formed in the platen surface, a discrete set of compartments inside the platen each fluidly coupled to a unique set of improved vacuum apertures, and vapor/dust recovery apertures fluidly coupled to a storage, collection, or other disposal vessel. In a preferred embodiment the present invention comprises at least four exhaust blowers each fluidly coupled to a discrete compartment within the platen and at least one said compartment connects to each end of the platen surface adjacent to the printing zone and is adapted to evacuate the entire interior space of a large format printing engine. In each of these embodiments, at least some of the improved vacuum apertures located near the edges of the printing zone extend to a recess, or grooved, segment of the platen surface. Also in each said embodiment of the present invention using a planar, or flat, printing zone, a set of gradually tapering transition platen sections promote the best vacuum seal between the platen (within the printing zone) and the printing media. These gradually tapering, or xe2x80x98radiusedxe2x80x99, transition sections can either be integrated into a monolithic platen member, or may be fabricated separately and suitably attached to the platen. In the latter example, the separately fabricated transition sections should preferably be fabricated of inexpensive light weight material to minimize cost and weight without impacting the printing performance of a large format ink jet print engine practicing the present invention. In the embodiments wherein one or more vapor evacuation aperture is ported to a vessel, an appropriate vapor recovery technique may be practiced to capture any potentially harmful vapors or print-artifact producing dust particles. In these embodiments, a suitable recovery technique might include fume incinerator(s), carbon adsorbers, HEPA-quality filter materials, phase change recovery, and the like.
Thus in the preferred embodiments, the inventive apparatus allows a high degree of control over the printing substrate within the printing zone by extending the effective xe2x80x9creachxe2x80x9d of certain vacuum apertures near the periphery of the printing zone without requiring extensive under-platen compartments while providing exceedingly consistent printing performance for each print head operating in a large format ink jet printer.
The following figures are not drawn to scale and only detail of a few representative embodiments of the present invention, more embodiments and equivalents of the representative embodiments depicted herein are easily ascertainable by persons of skill in the digital imaging arts.